Mapping Experiments: The methods of receptive field (RF) mapping and axonal transport of HRP will be used to detertmine the relations among cytoarchitecture, topographical organization, and interhemispheric connectivity within areas S-I ;and S-II/r of the cerebral cortex of macaque monkeys. The deleterious effects of general anesthetics on single neuron RFs and response to peripheral stimulation will be avoided by employing metal microelectrodes to obtain single neuron data from animals trained to accent gentle mechanical stimulation. For some animals single unit data will be obtained from zones homotopically related to HRP-infiltrated zones in the opposite hemisphere; the single unit data will then be reconstructed and related both to the pattern of HRP labelling and to cytoarchitecture. The method of metabolic mapping with 14C-2-deoxyglucose (2DG) will be used to provide an independent assessment of the relations between cytoarchitecture and cortical somatotopic organization. This method will also be used in combination with single unit recording techniques to investigate the meaning of the striplike pattern of cortical activation produced by somatic stimulation. Electrolytefilled micropipettes will be used to study the properties of neurons whose soma lie within the superficial layers of the S-I cortex; intracellular iontophoretic injection of HRP will be used to visualize cortical neurons with identified functional properties. Quantitative Experiments: Precisely controlled mechanical stimuli will be used to identify the dependency of the capacity of single S-I and S-II/r neurons to discriminate between stimuli moving in different directions or at different velocities. The objective of these experiments is to provide data bearing on the suggestion that similar neurons account for the capacities of hunans to carry out cutaneous direction and velocity discriminations. A final series of quantitative experiments will utilize dual moving tactile stimuli to deliver different spatial and temporal patterns of mechanoreceptor input to S-I and S-II/r neurons. It is anticipated that the latter studies will provide information about the mechanisms underlying cortical neuron directional sensitivity, and about the functional role of the highly ordered bilateral input that impings on many neurons within area S-II/r.